Denise Crosby = poor career choice
I consider it both a poor career choice and bad luck. Michael Dorn got even less than do as Worf than Crosby as Tasha in the first season, until
Heart of Glory, but he was smart enough to stick with the show.
Gates McFadden = victim of sexual harassment
I was quite shocked when I first heard that. Glad things worked out for her.
Diana Muldaur = fulfilled her obligation, then left amicably
Okay, I consider it not really bad luck for her since she never quite enjoyed being on the show.
Terry Farrell = left near the end of DS9 for a better opportunity (network sitcom) - good decision!
Farrell was trying to get a raise for her final season, but Paramount went behind her back and hired everyone else and ended up firing her. That just rubs me the wrong way. As a result of that, we wasted several episodes developing Ezri Dax during the last season.
Yes, she did end up doing a few seconds on Becker, but she was also abruntly fired from that show for no reason.
But I'm glad she seems to be happy these days as a mom.
Jennifer Lien = chose to leave for some reason (can't remember what it was).
Nope.
The VOY producers were planning to drop Garrett Wang in order to make the space for the hiring of Jeri Ryan. It was obvious they had no clue what to do with Harry Kim. But PEOPLE magazine put up a sexist people list which included Wang, so they decided to drop Lien instead.
I always liked Kes, so I was pretty pissed about that.